The present invention relates to a method and an apparatus for indicating the contact structure of an electromagnetic contactor on the housing thereof by burning numbers or other characters into the housing using laser light. In the present invention, the term " electromagnetic contactor" refers in particular but not exclusively to small-sized contactors such as electromagnetic relays.
FIG. 1 is a perspective view of a typical electromagnetic contactor of the type to which the present invention is directed, and FIG. 2 is a plan view of the same. In the figures, element number 1 is a contactor having an unillustrated movable core, a movable contact, a contact mechanism, and the like housed therein. Element number 2 is the housing of the contactor, the housing 2 having a plurality of electrically insulating barriers 3 secured to the top portion thereof on both of its sides. The insulating barriers 3 and the rest of the housing 2 are usually made of a phenolic resin. Between each barrier 3, fixed contacts 4 are secured to the housing 2 of the contactor 1 by screws 5 such that their contact surfaces which are contained within the housing 2 of the contactor 1 confront the contact surfaces of the above-mentioned movable contact. Element number 6 is a control terminal secured to the housing 2 of the contactor 1 by a screw 7. Via this control terminal 6, current is supplied to an unillustrated electromagnetic within the housing 2 which operates the movable contact of the contactor 1. As shown in FIG. 2, there is one control terminal 6 provided on each side of the contactor 1 at opposite ends. Elements number 8 and 9 are name plates which indicate the rating and other characteristics of the contactor 1.
This type of contactor 1 generally contains both normally open contacts, which close when the unillustrated electromagnet of the contactor 1 is energized, and normally closed contacts, which close when the electromagnet is energized. In recent years, it has become common to indicate the type of contacts (normally open or normally closed) contained within a contactor 1 by marking terminal numbers 10 on the electrically insulating barriers 3 adjoining the corresponding fixed contacts 4. The terminal numbers 10 are generally two-digit numbers, the last digit of which indicates the type of contact. For example, a two-digit number ending in a 1 or a 2 such as 21 or 22 indicates a normally closed contact, while one ending in a 3 or a 4 such as 13 or 14 indicates a normally open contact. As shown in FIG. 2, each fixed contact 4 is located directly opposite from a contact 4 of the same type on the opposite side of the contactor 1.
In the past, these terminal numbers 10 have been marked on the insulating barriers 3 by printing with ink. However, printing poses a number of difficulties. If the terminal numbers 10 are printed on the insulating barriers 3 prior to assembly of the contactor 1, great care must be taken during assembly to ensure that an insulating barrier 3 bearing the correct terminal number 10 is disposed next to the corresponding type of fixed contact 4. In the example shown in FIG. 2, since there are 8 different terminal numbers 10, this means that there are 8 different types of insulating barriers 3 which can be distinguished only by number. Assembly thus becomes complicated and costly, and improper assembly can easily take place. Furthermore, as the contents of the name plates 8 and 9 vary depending upon the combination of fixed contacts 4 in the contactor 1, a large different number of name plates must be prepared, making assembly even more complicated and increasing the chances of improper assembly increase.
On the other hand, if the terminal numbers 10 and the name plates 8 and 9 are printed on the housing 2 of a completely assembled contactor 1, the printing process itself becomes complicated; since the top surfaces of the insulating barriers 3 are not level, printing of the terminal numbers 10 and the name plates 8 and 9 generally has to be performed in 4 different steps, a different step being required for each of the name plates 8 and 9 and for the terminal numbers 10 on both sides of the contactor 1.
Furthermore, when the terminal numbers 10 and name plates 8 and 9 are printed on the housing 2, much preparatory time is required for the printing itself, for the maintenance of ink, and for the interchanging of printing blocks, and it is possible for the printed characters to be smudged or erased should they come into contact with some object before they are dry.